Spatially-resolved dissolution monitoring using AFM

Abstract

Continued lithographic scaling using high-NA EUV scanners requires materials and processes with sufficient resolution and stochastic performance to translate the aerial image into thin film photoresist material. Amongst these key processes is photoresist dissolution that converts latent exposure chemistry in the photoresist into a developed pattern. However, co-optimization of resist materials and the develop process is difficult due to the challenge of directly measuring resist dissolution at the nanometer spatial and sub-second temporal scales on which it occurs. Most metrology of the dissolution process thus ignores either the temporal component by measuring just the final developed structure, or the spatial component as is done in most dissolution rate monitoring experiments. To overcome these challenges, we have developed an in-situ dissolution rate monitoring technique using high-speed atomic force microscopy (AFM). As opposed to pioneering work using AFM to monitor the dissolution process, our technique incorporates the use of a specially-designed flow cell which provides precise control of the time at which developer is introduced to the photoresist material, as well as delivery of nearly full-strength developer in fractions of a second. Our system thus offers the ability to probe the spatially-dependent nature of the dissolution process at conditions close to those in the fab, providing insight into exposure-dependent dissolution rate gradient, material swelling, and other potentially lithographically relevant phenomena such as polymer entanglement. In doing so, we provide another technique to aid in the design and study of photoresist materials for future lithographic nodes.

Lithography in a quantum world

“…This is a topic studied a few decades ago, 40,41) but since then there have been few studies of resist development until recently. 42) These new studies of the development of chemically amplified resists could prove important for understanding the lithography of contacts and vias. 43) More studies on the development of EUV resists will likely be useful, including those that focus on the development of non-CARs, as the limited research in this area indicates that greater capability might be attained by considering the resist development process.…”

Relationship between poly(4-hydroxystyrene) (PHS) and tetramethylammonium hydroxide (TMAH) concentrations during the development of PHS films in TMAH aqueous solution studied by a quartz crystal microbalance (QCM) method

“…3) In the high-volume production of semiconductor devices, 2.38 wt% tetramethylammonium hydroxide (TMAH) aqueous solution has been used as a standard developer. The dissolution kinetics of resist films have been widely investigated by visible and infrared reflectance spectroscopy, 4) high-speed atomic force microscopy [5][6][7] and a quartz crystal microbalance (QCM) method. 4,[8][9][10][11] Chemically amplified resists have been used in semiconductor lithography.…”